(1) Field of the Invention
This invention is related to the crank axle of a bicycle crank assembly and is particularly related to a crank axle of fiber-reinforced construction and to the connection between a fiber-reinforced crank axle and a crank arm.
(2) Description of the Related Art
A bicycle crank assembly or crankset has traditionally been designed as a 3-piece assembly consisting of a crank axle, a left crank arm, and a right crank arm. The left crank arm is connected to the left end of the crank axle via a system of straight and/or tapered splines in combination with a fixing bolt to secure the connection. Likewise, the right crank arm is connected to the right end of the crank axle in a similar arrangement. The crank axle is radially supported and axially located by two axially spaced bearing assemblies that are located axially inboard of the crank arms. The drive sprockets, or chainrings, are mounted to the right crank arm via a “spider”, which consists of a series of radial arms extending between the chainring and the axle end of the right crank arm. The crank axle is generally made of steel, while the crank arms are usually of solid aluminum construction.
More recently, some state-of-the-art designs are arranged such that the steel crank axle is permanently fixed to the right crank arm. In addition, some high-end crank arms utilize carbon fiber reinforced material in their construction. However, these crank assemblies still utilize crank axles made of steel, which is a very high-density material, and results in a crank axle that is quite heavy.
There have been some prior art cranksets that utilize a split crank axle, where a left crank axle portion is removably connected to a right crank axle portion at a connection interface that is located axially inboard from the two supporting bearings. In such designs, the left crank arm is integrally joined to the left crank axle portion and the right crank arm is integrally joined to the right crank axle. Such a connection may be considered a structural interruption of the crank axle and this type of design places this connection at a very highly stressed region of the crank axle, which may result in a weaker and/or heavier connection. Additionally, this region also has severe geometric constraints due to the surrounding bottom bracket shell (not shown) of the bicycle frame. This serves to limit the structural geometry necessary to create a strong and lightweight connection. Further, since the region of connection is completely enclosed by the bottom bracket shell and the bearings, access and means to operate the connection are severely limited. This results in further constraints on the design of this connection and further limits the ability to create a rigid, strong and lightweight connection. Needless to say, such designs have had only limited success in the marketplace.
In addition, the connection between the crank arm(s) is somewhat complex and requires the expense of precision machining and additional manufacturing steps to achieve a reliable connection. Further, this connection requires additional components, such as fixing bolt(s), which add cost and weight to the overall assembly.
Further objects and advantages of the present invention will appear hereinbelow.